My favorite area is Yodelin, which is the first overflow parking area east of Stevens Pass, going eastbound on US2. Just hike up behind the building there and you'll hit an obvious old road cut. You switchback a bit, but the goal is to head southeast around the mountain to where the old ski runs used to be. The tree skiing there is phenominal and if you stay in those trees, you can pretty much ski it in all conditions. Just watch out while crossing open slopes, but you can avoid most of those anyway.